Reactions and Solution Stoichiometry AP Chem - Unit 2 Reactions and Solution Stoichiometry

Types of Reactions Combination (Synthesis) Decomposition Combustion Single Replacement Double Replacement (Metathesis)

Combination/Synthesis Basic Form A + B  AB Rxns of elements with oxygen and sulfur C(s) + O(s)  CO2 (g) Rxns of metals with halogens 2Na(s) + Cl2 (g)  2NaCl Synthesis rxns with oxides CaO(s) + H2O (l)  Ca(OH)2 (s)

Decomposition Basic Form AB  A + B Binary compounds 2H2O (l)  2H2 (g) + O2 (g) Metal hydroxides Cu(OH)2 (s)  CuO(s) + H2O (l)

More Decomposition Examples Metal carbonates PbCO3 (s)  PbO (s) + CO2 (g) Metal chlorates 2KClO3 (s)  2KCl (s) + 3O2 (g) Oxyacids H2CO3 (l)  H2O (l) + CO2 (g)

Combustion A substance combines with oxygen, releasing a large amount of energy in the form of light and heat. True or False: The products of every combustion reaction are CO2 and H2O False

Combustion Examples Reactive elements combine with oxygen P4(s) + 5O2(g)  P4O10(s) (This is also a synthesis reaction) The burning of natural gas, wood, gasoline C3H8(g) + 5O2(g)  3CO2(g) + 4H2O(g)

Single Replacement Basic Form A + BY  AY + B Metals by other metals 3Mg + 2FeCl3  2Fe + 3MgCl2 Hydrogen in water by another metal 2Na +2H2O  H2 + 2NaOH

More Single Replacement Hydrogen in an acid by another metal 2Li + 2HCl  H2 + 2LiCl Halogens by more active halogens Cl2 + 2KI  I2 + 2KCl

The Activity Series of the Metals Lithium Potassium Calcium Sodium Magnesium Aluminum Zinc Chromium Iron Nickel Lead Hydrogen Bismuth Copper Mercury Silver Platinum Gold Metals can replace other metals provided that they are above the metal that they are trying to replace. Metals above hydrogen can replace hydrogen in acids. Metals from sodium upward can replace hydrogen in water

The Activity Series of the Halogens Fluorine Chlorine Bromine Iodine Halogens can replace other halogens in compounds, provided that they are above the halogen that they are trying to replace. 2NaCl(s) + F2(g)  2NaF(s) + Cl2(g) MgCl2(s) + Br2(g)  ??? No Reaction

Double Replacement (Metathesis) Basic Form AX + BY  AY + BX One of the compounds formed is usually a precipitate, an insoluble gas that bubbles out of solution, or a molecular compound, usually water. How do you tell if a precipitate will form? Use your Solubility Rules!!!

Mostly Soluble Ion Solubility Exceptions NO3- Soluble None ClO4- Na+ K+ NH4+ Cl-, I- Pb2+, Ag+, Hg22+ SO42- Ca2+, Ba2+, Sr2+, Pb2+, Ag+, Hg2+

Mostly Insoluble Ion Solubility Exceptions CO32- Insoluble Group IA and NH4+ PO43- OH- Group IA and Ca2+, Ba2+, Sr2+ S2- Groups IA, IIA, and NH4+

The Solubility Rule Song!!!! (Sing to Rhythm of 99 Bottles)  Alkali metals and ammonium salts,Whatever they may be, Can always be depended on for solubility When asked about the nitrates The answer is always clear, They each and all are soluble, Is all we want to hear. Most every chloride's soluble At least we've always read Save silver, mercury one And chloride of lead Every single sulfate Is soluble, 'Tis said 'Cept barium, strontium, mercury one And calcium and lead. - Hydroxides in general don't dissolve at all But, barium, strontium and calcium Are slightly soluble *but don't forget * Alkali metals and ammonium salts Whatever they may be Can always be depended on For solubility  The carbonates are insoluble, It's lucky that it is so, Or else, our marble buildings Would melt away like snow. *but, once again, don't forget * For solubility

Spectator Ions do NOT participate in the reaction Net Ionic Equations Written to show only the species that react or undergo change in aqueous solution. Steps for writing net ionic equations Write a balanced molecular equation Rewrite the equation to show the ions that form in solution Identify and cancel spectator ions Spectator Ions do NOT participate in the reaction

Sample Problem What compound precipitates when solutions of Fe2(SO4)3 and LiOH are mixed? Write the complete chemical reaction for the reactants above. Write the net ionic equation. List any spectator ions.

Another Type of Metathesis Acid/Base Reactions Two Types Neutralization HCl + NaOH  NaCl + H2O Gas Formation 2HCl +Na2S  H2S(g) + 2NaCl HCl + NaHCO3  NaCl + H2CO3 H2CO3  H2O + CO2(g)

Oxidation Reduction Rxns Electrons are transferred Oxidation = Loses Electrons Reduction = Gains Electrons OIL RIG LEO goes GER!! OR

Redox Rxn Each sodium atom loses one electron atom gains one electron: Each chlorine atom gains one electron:

LEO says GER : Lose Electrons = Oxidation Sodium is oxidized Gain Electrons = Reduction Chlorine is reduced

OIL RIG: Oxidation Is Loss of electrons Sodium is oxidized Reduction Is Gain of electrons Chlorine is reduced

Reducing Agents and Oxidizing Agents The substance reduced is the oxidizing agent The substance oxidized is the reducing agent Sodium is oxidized – it is the reducing agent Chlorine is reduced – it is the oxidizing agent

Rules for Assigning Oxidation #s Atoms in elemental form are always zero Monatomic ions equal the charge on the ion Oxygen is usually -2 (except peroxide is -1) Hydrogen is +1 with NM and -1 with M Fluorine is always -1 Sum of the ox #s of all atoms in a neutral compound is zero Sum of the ox #s in a polyatomic ion = the ion charge

Sample Problem H2S S8 SCl2 Na2SO3 SO42- Determine the oxidation #s for the following: H2S S8 SCl2 Na2SO3 SO42-

Oxidation of metals by acids and salts Similar to single replacement rxns, sometimes called Displacement Rxns General form A + BX  AX + B Examples Zn(s) + 2HBr (aq)  ZnBr2(aq) + H2 (g) Mn(s) + Pb(NO3)2(aq)  Mn(NO3)2 (aq)+ Pb(s)

Rules for Balancing Redox Rxns Assign oxidation #s Determine which species are being oxidized or reduced Divide the equation into 2 half-reactions Balance each half reaction Balance elements other than H and O Balance O by adding water as needed Balance H by adding H+ as needed Balance charge by adding e- Multiply half reactions by integers so # of e- are the same in each reaction Add half reactions together, simplifying when you can Check to see if equation is charge and mass balanced

Sample Problem Balance the following MnO4-(aq) + C2O42-(aq) Mn2+(aq) + CO2(aq)

Other Rxns Metal Oxide in Water Nonmetal Oxide in Water MO + H2O  MOH BaO + H2O  Ba(OH)2 Nonmetal Oxide in Water NO + H2O  oxyacid N2O3 + H2O  HNO2

Solutions

Solute Solvent A solute is the dissolved substance in a solution. Salt in salt water Sugar in soda drinks Carbon dioxide in soda drinks Solvent A solvent is the dissolving medium in a solution. Water in salt water Water in soda

Definition of Electrolytes and Nonelectrolytes An electrolyte is: A substance whose aqueous solution conducts an electric current. A nonelectrolyte is: A substance whose aqueous solution does not conduct an electric current. Try to classify the following substances as electrolytes or nonelectrolytes…

Which of the following are electrolytes? Pure water Tap water Sugar solution Sodium chloride solution Hydrochloric acid solution Lactic acid solution Ethyl alcohol solution Pure, solid sodium chloride

Answers… ELECTROLYTES: NONELECTROLYTES: Tap water (weak) NaCl solution   HCl solution   Lactate solution (weak)   Pure water   Sugar solution   Ethanol solution   Pure, solid NaCl

Electrolytes & Net Ionic Equations Ionic CompoundsDissociate NaCl(s)  Na+(aq) + Cl-(aq) AgNO3(s)  Ag+(aq) + NO3-(aq) MgCl2(s)  Mg2+(aq) + 2 Cl-(aq) Na2SO4(s)  2 Na+(aq) + SO42-(aq) AlCl3(s)  Al3+(aq) + 3 Cl-(aq) These compounds should be written as ions in net ionic equations.

Strong acids such as HCl are completely ionized in solution Strong acids such as HCl are completely ionized in solution. So they are written as ions in the net ionic equation Other examples of strong acids include: Sulfuric acid, H2SO4 Nitric acid, HNO3 Hydriodic acid, HI Perchloric acid, HClO4 Weak acids such as lactic acid usually ionize less than 5% of the time. So they are not written as ions in the net ionic equation.

Molarity The concentration of a solution measured in moles of solute per liter of solution. mol = M L

Sample Problem How many grams of sodium chloride are needed to prepare 1.50 liters of 0.500 M NaCl sol’n?

Serial Dilution It is not practical to keep solutions of many different concentrations on hand, so chemists prepare more dilute solutions from a more concentrated “stock” solution. MstockVstock = MdiluteVdilute

Sample Problem What volume of stock (11.6 M) hydrochloric acid is needed to prepare a 3.0 M - 250. ml solution?

Sample Problem How many grams of Ca(OH)2 are needed to neutralize 25.0 mL of 0.100 M HNO3?

Sample Problem A sample of 70.5 mg of potassium phosphate is added to 15.0 mL of 0.050 M silver nitrate, resulting in the formation of a precipitate. Write the molecular equation for the reaction What is the limiting reactant? Calculate the theoretical yield, in grams, of the ppt that forms.

Sample Problem 45.7 mL of 0.500 H2SO4 is required to neutralize a 20.0 mL sample of NaOH solution. What is the concentration of the NaOH solution?